Self-breakable yield point enhancer for oil based drilling mud

ABSTRACT

The present invention relates to a liquid, self-breakable, temporary viscosifier agent (yield point enhancer) for oil based drilling muds, obtained by reacting one or more dicarboxylic fatty acids with a secondary dialkanolamine and thereafter with a tertiary tialkanolamine, and to oil based drilling muds containing it.

TECHNICAL FIELD

The present invention relates to a liquid, self-breakable, temporaryviscosifier agent (yield point enhancer) for oil based drilling muds,obtained by reacting one or more dicarboxylic fatty acids with asecondary dialkanolamine and thereafter with a tertiary trialkanolamine.

Drilling systems involve the use of two main kinds of mud: water basedmud (WBM) and oil based mud (OBM).

Water-in-oil emulsions muds, or inverted emulsion muds, are the mostused OBM.

Drilling muds (or drilling fluids) are very complex system; they involvethe use of different chemicals such as emulsifiers, wetting agents,brines, oils, rheological modifiers, fluid loss control additives andweighting agents.

The mud performs a number of functions, such as removing drill cuttings,lubricating the bit, coating the wellbore surface to avoid flow offluids in and out of the wellbore, helping to support the weight of thedrill pipe and casing.

In today's operations, drilling fluids are pumped under great pressurethrough a long pipe, reach the very bottom of the drill hole through thecenter of the drilling bit, then they are returned to the surfacethrough the small annulus between the outside of the pipe itself and theborehole wall or casing.

The theoretical perfect drilling fluid is pseudoplastic, showing a lowviscosity when sheared, such as under agitation or circulation, butthickening when the shearing action is stopped, holding cuttings inplace and avoiding sagging; the fluid should thicken rapidly, reaching asufficient gel strength before suspended material settles out.

This behavior should be reversible independently from the temperature.

Therefore drilling muds require the addition of one or more rheologymodifiers to maintain proper viscosity and stability.

Oil based drilling muds, and particularly those designed for offshoredeep water drilling, are mainly water-in-oil emulsions of mineral oils,or olefins or paraffins or mixture thereof.

A major constituent of these oil based drilling fluids are organophilicclays: large amounts of colloidal or gelling agents are required toobtain the desired rheology of the mud and organophilic clays mostlyperform these action while operating.

A fairly big amount of clays is usually necessary to give the desiredpseudoplastic properties to the mud.

The solids added to the mud are usually intended to increase thespecific gravity of the mud itself: during drilling operations thecounter-pressure of the oil or gas from reservoir can be very high and ahigh density drilling fluid is always recommended. One of the mostutilised weighting agents is barite.

OBM for offshore drilling are generally prepared on dry land and thenshipped to the platforms; they should therefore be stable for quite along time, during transportation and until they reach their operativesite.

Unfortunately it is very difficult to activate (swell) the organophilicclays during the preparation of the mud; a high shear might be used toprovide heat and help the swelling of the clays, but most plants do nothave the appropriate equipment.

Therefore it is normally necessary to add to the mud a yield pointenhancer which is able to temporarily emulate the function of the claysuntil they develop their full viscosity.

BACKGROUND ART

Many yield point enhancer are known, such as the amide resin additivesdisclosed in U.S. Pat. No. 4,816,551.

Oil based muds containing such amide resin additives exhibit high solidscarrying capacity but also show increasing values of viscosity whenexposed to low temperatures; their use for off-shore deep sea drillingoperation is therefore mostly critical.

For offshore operation the low temperature of the sea is always to betaken into account, as the effect of the yield point enhancers isusually strongly dependent from temperature (the lowest the temperature,the highest the risk of undesired gelling of the mud).

Drilling operations are not continuous processes; many stops mustnecessarily take place and it is then that the risk of an excessiveviscosity of the mud, due to the presence of a yield point enhancer, cancreate serious problems.

When drilling operation takes place in non-deep water, particularcaution and additional tests are required to correctly dose the yieldpoint enhancer.

When deep water drilling operations are performed, the temperature ofthe sea falls near to zero Celsius degrees, and the risk of gelling ofthe mud is very high, especially during stops.

It would therefore be highly desirable to find a self-breakable yieldpoint enhancer for oil based drilling muds showing high solids carryingcapacity during transportation and whose viscosifying effect ceases assoon as drilling actually takes place, thus leaving the rheology controlof the mud to the organophilic clays.

DISCLOSURE OF INVENTION

According to a fundamental aspect of the invention, it has now beenfound that, a yield point enhancer obtained from the reaction of one ormore dicarboxylic fatty acids with a secondary dialkanolamine andthereafter with a tertiary trialkanolamine, even when dosed in smallquantities, provides to oil based drilling muds high solids carryingcapacity during transportation, preventing the settling out of thesolids from the moment of the preparation of the mud until the mudreaches its working destination.

The yield point enhancer of the invention emulates the properties of aswollen organophilic clay, giving temporarily to the mud high yieldpoint and gel strength without increasing the plastic viscosity.

This effect disappears during drilling operation, releasing the totalcontrol of the rheological properties to the organophilic clay andwithout further modifying the rheological properties of the oil basedmud.

The yield point enhancer of the invention is able to thicken the mudeven when low viscosity oils are used as the external phase of theinverted emulsion; it provides a high yield point, a quick way to reacha high gel strength, while maintaining a low plastic viscosity.

According to a fundamental aspect, the yield point enhancer of theinvention is an ester amide obtained reacting one or more dicarboxylicfatty acids with a secondary dialkanolamine and thereafter with atertiary trialkanolamine.

The yield point enhancer of the invention is prepared by a two stepprocess.

In the first step about one molar equivalent of the dicarboxylic fattyacids is reacted with about one molar equivalent of the secondarydialkanolamine, preferably of diethanolamine.

In the second step, the intermediate is reacted with about one third ofmolar equivalent of a tertiary trialkalkanolamine, preferably oftriethanolamine, to obtain the desired ester amide.

In both steps water is collected and eliminated from the reactionvessel.

The first step of the process is performed at about 150° C., andexternal heating is required; preferably, the dialkanolamine is slowlyadded into a reaction vessel where the dicarboxylic acid has previouslybeen charged; and the reaction mixture is kept stirred until about onemolar equivalent of water is collected.

No isolation of the intermediate is required.

The second steps is lightly exothermic and the reaction is carried onpreferably at 120-150° C. by slowly adding the trialkanolamine; thereaction mixture is kept stirred until about one molar equivalent ofwater is collected.

Both steps are preferably carried on in the presence of a solvent.

The preferred solvents are glycols, gycol ethers, or mixture thereof; wecite as examples of suitable solvents: diethylene glycol mono-n-butylether, diethylene glycol ethyl ether, ethylene glycol mono-n-butylether, butoxytriglycol.

The most preferred glycol ether is butoxytriglycol.

Optionally, to adjust the viscosity of the final product, one or moresuitable diluents, such as propylene carbonate or a glycol or glycolether (such as those cited above as suitable solvents), or mixturethereof, can be added after step (ii).

Preferably, the total quantity of solvent and diluent in the yieldenhancer according to the invention is from 30 to 70 wt %, morepreferably from 40 to 60 wt %.

The dicarboxylic fatty acids useful for the realization of the inventionare those having general formula HOOC—R—COOH, wherein R is an alkylenegroup containing from 10 to 50 carbon atoms, preferably from 20 to 40carbon atoms.

The secondary dialkanolamine has the general formula HO—R′—NH—R′OH,wherein R′ is an alkylene group containing from 1 to 6 carbon atoms.

The tertiary trialkanolamine has the general formula N(—R″OH)₃, whereinR″ is an alkylene group containing from 1 to 6 carbon atoms.

The preferred dicarboxylic fatty acids are dimerized fatty acids,commercial products prepared by dimerization of unsaturated fatty acidscontaining from 8 to about 18 carbon atoms, including 9-dodecenoic(cis),9-tetradecenoic(cis), 9-octadecenoic(cis), octadecatetranoic acids andthe like.

Mixtures of dimerized fatty acids may be used.

The preferred secondary dialkanolamine are diethanolamine,diisopropanolamine, and mixtures thereof; diethanolamine is the mostpreferred secondary dialkanolamine.

The most preferred tertiary trialkanolamine is triethanolamine, but alsoother tertiary alkanolamines can be used, such as tri-iso-propanolamine,and mixtures of triethanolamine and tri-iso-propanolamine.

The ester amide of the invention can be added to the drilling mud at anystage of its preparation and the method of its introduction in the mudis not critical.

Advantageously, the yield point enhancers of the invention are used forthe stabilisation of oil based drilling muds for off-shore deep waterdrilling operation.

They impart to such muds excellent stability and, being in liquid form,they can be readily dosed.

Another fundamental object of the present invention is an oil baseddrilling mud containing from 0.05 to 1.0% wt, preferably from 0.1 to0.5% wt, of the yield point enhancer obtained as described above, byreacting one or more dicarboxylic fatty acids with a secondarydialkanolamine and thereafter with a tertiary trialkanolamine, thepercentages being referred to a yield point enhancer of the inventionhaving a total content of solvent and diluent of 50 wt %

According to a preferred embodiment of the invention, the oil baseddrilling mud is an oil based inverted emulsions, formed by an oilycontinuous external phase and an aqueous internal phase.

In order to prepare the oil based drilling mud of the invention, watersoluble salts, chosen among sodium chloride, potassium chloride, sodiumbromide or calcium chloride, are normally added to the oily phase in theform of brines, in concentration between 1 to 50% vol, preferablybetween 10 to 30% vol, more preferably in concentration of 25% vol (%vol is referred to the final emulsion).

The man skilled in the art is able to determine the appropriate brine tooil ratio, in order to obtain a stable emulsion, while considering andlimiting the cost of the drilling fluid.

The oil based drilling mud of the invention normally also contains oneor more surfactants (emulsifiers), to stabilise the emulsion; thesurfactants can be added to the external phase, to the internal phase orto both phases.

Useful emulsifiers include, rosin acids, tall oil acids and derivativesthereof (such as amido-amines and imidazolines), fatty alcohols andfatty acids, such as oleic acid, caproic acid, stearic acid.

Various modifications and alterations to this invention will becomeapparent to those skilled in the art without departing from the scope ofthis invention.

It should be understood that this invention is not intended to be undulylimited by the illustrative embodiments and examples set forth herein.

BRIEF DESCRIPTION OF DRAWINGS

In FIG. 1-6 the results of the application tests (Examples 3 and 4)carried on with oil based drilling muds according to the invention(prepared as described in Example 2) are reported.

FIG. 1-3 show the decrease of the yield point of oil based drilling mudsaccording to the invention (D, O, MO) in comparison with the yield pointof the analogous muds not containing the yield point enhancer of theinvention (blanks: Do, Oo, MOo), when muds are exposed to shear stress(see Example 3).

FIG. 4-6 show the decrease of the yield point of oil based drilling mudsaccording to the invention (D, O, MO) in comparison with the yield pointof the analogous muds not containing the yield point enhancer of theinvention (blanks: Do, Oo, MOo), when muds are exposed to heat (seeExample 4).

EXAMPLE 1

Preparation of the Yield Point Enhancer (YPE1)

736.56 g of dimer acid (1.37 mol) (Unydime® T18, Arizona Chem. Co., US)are charged in a reaction vessel; 405 g of butoxytriglycol are thenadded the reaction vessel and the mixture is heated up to 95° C. whilestirring. 144.36 g of diethanolamine are then slowly added and thetemperature is maintained at about 150° C., until 24.66 g of water iscollected.

68.40 g of triethanolamine (0.46 mol) are then slowly added; thereaction is slightly exothermic and the temperature is maintained atabout 150° C., purging with a moderate flow of nitrogen and collectingwater until 24.66 g of water is collected

The reaction mixture is then cooled down to 95° C. and 405 g ofbutoxytriglycol and 90 g of propylene carbonate are added, obtaining1800 g of final product.

The final product (YPE1) is a amber homogeneous liquid; IR analysisshows a typical amide band at 1627 cm⁻¹ and an ester band at 1739 cm⁻¹.

EXAMPLE 2

Preparation of the Oil Based Muds

The muds are prepared by mixing 158.34 g of organic phase (Diesel, or aninternal olefin mixture C16-C18, or a mineral oil) and 82.443 g of 25%wt CaCl₂ brine and then emulsifying in the presence of an organophilicclay, lime, an imidazoline based primary emulsifier, Ecotrol® (fluidloss reducer from M-I L.L.C, US), barite, and YPE1.

The composition of the muds (in g) is reported in Table 1.

TABLE 1 D Do O Oo MO MOo Diesel 158.34 158.34 IO 16-18⁽¹⁾ 158.34 158.34M.O.⁽²⁾ 158.34 158.34 25% CaCl2 82.44 82.44 82.44 82.44 82.44 82.44O.C.⁽³⁾ 4 4 4 4 4 4 Lime 3 3 3 3 3 3 Im⁽⁴⁾ 8 8 8 8 8 8 Ecotrol 0.5 0.50.5 0.5 0.5 0.5 Barite 185 185 185 185 185 185 YPE1 1 0.00 0.5 0.00 20.00 ⁽¹⁾Internal olefin mixture C16-C18 ⁽²⁾Mineral oil ⁽³⁾OrganophilicClay ⁽⁴⁾Imidazoline based primary emulsifier

Application Tests.

EXAMPLE 3

The yield point of the muds sheared at 8000 rpm with Hamilton Beach ismeasured at 25° C. at intervals.

The results are reported in Table 2, and as a graph, in FIG. 1-3.

TABLE 2 Yield Point time (min) D Do O Oo MO MOo 1 55 22 18 8 9 4 5 58 2918 10 12 4 10 58 29 18 11 12 4 30 57 30 19 10 11 4 50 57 29 20 11 11 470 58 30 21 11 11 5 90 54 31 21 10 10 4 110 52 30 20 11 9 4 130 49 30 2011 9 5 150 47 30 18 11 8 5 170 46 29 16 10 8 4 190 43 31 14 11 8 5 21038 29 12 11 7 5 230 34 29 11 11 6 5 250 30 30 11 11 5 5

EXAMPLE 4

The muds are heated to 65° C. under low shear condition and their yieldpoint is measured at intervals of 10 minutes.

The results are reported in Table 3, and as a graph, in FIG. 4-6.

TABLE 3 Yield Point time (min) D Do O Oo MO MOo 20 13 5 9 4 — — 40 13 410 4 6 2 60 14 5 9 4 6 2 80 12 5 10 4 6 2 100 12 4 9 5 5 1 120 9 5 8 4 52 140 9 5 6 4 5 2 160 8 5 7 5 4 1 180 7 5 6 3 4 2 200 6 4 6 4 4 2 220 55 5 4 3 2 240 5 — 4 4 2 2

The application tests show that the yield point enhancer of theinvention, both under shear stress and heat (simulation of drillingoperating conditions), breaks down without changing any properties ofthe original mud.

1. A yield point enhancer for use in oil based drilling muds comprisingthe product obtained from a process comprising: in a first step, (i)reacting: about one molar equivalent of one or more dicarboxylic fattyacids having a general formula HOOC—R—COOH wherein R is an alkylenegroup containing from 10 to 50 carbon atoms, with about one molarequivalent of a secondary dialkanolamine having the general formulaHO—R′—NH—R′OH wherein R′ is an alkylene group containing from 1 to 6carbon atoms, at about 150° C. while collecting water and keeping thereaction mixture stirred until about one molar equivalent of water iscollected to form an intermediate; and in a second step (ii), reacting,the intermediate with about one third of a molar equivalent of atertiary trialkanolamine having the general formula N(—R″OH)₃ wherein R″is an alkylene group containing from 1 to 6 carbon atoms, at 120-150° C.while collecting water and keeping the reaction mixture stirred untilabout one molar equivalent of water is collected.
 2. The yield pointenhancer according to claim 1, wherein the yield point enhancer is anester amide.
 3. The yield point enhancer according to claim 1, wherein Ris an alkylene group containing from 20 to 40 carbon atoms.
 4. The yieldpoint enhancer according to claim 3, wherein the dicarboxylic fattyacids are dimerized fatty acids prepared by dimerization of unsaturatedfatty acids containing from 8 to about 18 carbon atoms.
 5. The yieldpoint enhancer according to claim 4, wherein the secondarydialkanolamine is diethanolamine and the tertiary trialkanolamine istriethanolamine.
 6. The yield point enhancer according to claim 5,obtained by performing steps (i) and (ii) in the presence of a compoundselected from the group consisting of glycols, glycol ethers, andmixtures thereof.
 7. The yield point enhancer according to claim 6,wherein steps (i) and (ii) are performed in the presence of a glycolether selected from the group consisting of diethylene glycolmono-n-butyl ether, diethylene glycol ethyl ether, ethylene glycolmono-n-butyl ether, butoxytriglycol, and mixtures thereof.
 8. The yieldpoint enhancer according to claim 7, wherein the glycol ether isbutoxytriglycol.
 9. The yield point enhancer according to claim 7,further comprising the product obtained by admixing the product of step(ii) with a diluent.
 10. The yield point enhancer according to claim 9,wherein the diluent is selected from the group consisting of diethyleneglycol mono-n-butyl ether, diethylene glycol ethyl ether, ethyleneglycol mono-n-butyl ether, butoxytriglycol, propylene carbonate andmixtures thereof.
 11. The yield point enhancer according to claim 10,wherein the diluent is present at a concentration of from 30 to 70% wt.12. An oil based drilling mud comprising from about 0.025 to about 0.5%wt of a yield point enhancer, the yield point enhancer being obtainedfrom a process comprising: in a first step, (i) reacting: about onemolar equivalent of one or more dicarboxylic fatty acids having ageneral formula HOOC—R—COOH wherein R is an alkylene group containingfrom 10 to 50 carbon atoms, with about one molar equivalent of asecondary dialkanolamine having the general formula HO—R′—NH—R′OHwherein R′ is an alkylene group containing from 1 to 6 carbon atoms, atabout 150° C. while collecting water and keeping the reaction mixturestirred until about one molar equivalent of water is collected to forman intermediate; and in a second step (ii), reacting, the intermediatewith about one third of a molar equivalent of a tertiary trialkanolaminehaving the general formula N(—R″OH)₃ wherein R″ is an alkylene groupcontaining from 1 to 6 carbon atoms, at 120-150° C. while collectingwater and keeping the reaction mixture stirred until about one molarequivalent of water is collected.
 13. The oil based drilling mudaccording to claim 12, wherein the oil based drilling mud is preparedusing a 1:1 wt % admixture of the yield point enhancer and a diluent.14. The oil based drilling mud according to claim 12, wherein the yieldpoint enhancer is an ester amide.
 15. The oil based drilling mudaccording to claim 12, wherein R is an alkylene group containing from 20to 40 carbon atoms.
 16. The oil based drilling mud according to claim15, wherein the dicarboxylic fatty acids are dimerized fatty acidsprepared by dimerization of unsaturated fatty acids containing from 8 toabout 18 carbon atoms.
 17. The oil based drilling mud according to claim16, wherein the secondary dialkanolamine is diethanolamine and thetertiary trialkanolamine is triethanolamine.
 18. The oil based drillingmud according to claim 17, wherein the yield point enhancer is obtainedby performing steps (i) and (ii) in the presence of a compound selectedfrom the group consisting of glycols, glycol ethers, and mixturesthereof.
 19. The oil based drilling mud according to claim 18, whereinthe glycol ether is butoxytriglycol.
 20. An oil based drilling mudaccording to claim 12, wherein the oil based drilling mud is in the formof inverted emulsion.